This invention relates to a process for the removal of calcium from calcium-containing petroleum crudes, heavy hydrocarbonaceous residua or solvent deasphalted oils derived from crudes and residua using carbonic acid as an extraction agent. A few, but increasingly important, petroleum crude feedstocks and residua contain levels of calcium which render them difficult, if not impossible, to process using conventional refining techniques. Specifically, the calcium contaminants causing particular problems are in the form of nonporphyrin, organometallically-bound compounds. These species have been only recently discovered in crude oils, very heavy crude oils in particular, and are apparently relatively rare. One possible class of calcium-containing compounds identified in particular is the calcium naphthenates and their homologous series. These organo-calcium compounds are not separated from the feedstock by normal desalting processes. The particular problem caused by them in a conventional refining technique is the very rapid deactivation of hydroprocessing catalysts. Examples of feedstocks demonstrating objectionably high levels of calcium compounds are those from the San Joaquin Valley in California. Generally, these crudes are contained in a pipeline mixture referred to as San Joaquin Valley crude or residuum.
The problems presented by calcium in petroleum feedstocks and their necessity for removal have only been recently appreciated, and the prior art contains few references specifically to its removal. Metals removal generally using organic compounds, however, has been addressed in the prior art, specifically for the removal of known metallic contaminants, such as nickel, vanadium, and/or copper, which are also ordinarily found in feedstocks as porphyrins, and other organometallic compounds.
In U.S. Pat. No. 3,052,627, Lerner, metals-contaminants are removed from crude petroleum feedstocks using a 2-pyrrolidone-alcohol mixture. In U.S. Pat. No. 3,167,500, Payne, metallic contaminants, such as metal-containing porphyrins, are removed from petroleum oils using a condensed polynuclear aromatic compound having a preferred C/H ratio and a molecular weight ordinarily called pitch binders. In U.S. Pat. No. 3,153,623, Eldib et al, selected commercially available organic compounds of high dielectric strength were added to assist in the electrically directed precipitation removing metals with the polar organic molecules.
It has now been unexpectedly found that the calcium-containing contaminants may be effectively removed from the feedstocks of the present invention by binding the calcium compounds using carbonic acid and its salts.